1. Field of the Invention
The present invention relates to a socket for an electrical part for use, for example, in testing the electrical part after mounting the electrical part such as semiconductor device or the like on the socket, more particularly, relates to an improvement of a socket for an electrical part in which a contact pin having an elastic piece, which is inserted into through holes of both a socket body and a movable member and is elastically deformable when the movable member is moved.
2. Related Art of the Invention
In a known art, there has been provided a socket for an electrical part for use such as in testing an electrical part by electrically connecting the electrical part such as a semiconductor device (hereinafter called “IC package”) etc. to a wiring board. Such conventional socket has, for example, a socket body placed on the wiring board, a movable member movably disposed on the socket body, contact pins each inserted into respective through holes formed in both the socket body and the movable member. The contact pin has a lower edge portion which is connected to an electrode of the wiring board and a contact portion provided at its upper edge portion, which is contacted to a terminal of the electrical part.
The lower edge portion side of the contact pin is fixed to the socket body and the upper edge portion thereof is provided with the contact portion designed to be contacted to the terminal of the electrical part. Further, a portion between the upper edge portion and the lower edge portion is designed to be elastically deformable (this portion is called hereinafter the “elastic piece”). When the movable member is moved, this elastic piece is elastically deformed such that the contact portion of the contact pin is contacted to the terminal of the electrical part by using this resulting elastic force.
Such type of known contact pins has a pair of elastic contact pieces extending in parallel. A pressed portion is provided on at least one of the elastic contact pieces for opening and closing the elastic piece. When the pressed portion is pressed by the movable member, one of the elastic pieces is structured to be opened or closed with respect to the other elastic piece (for example Patent document 1: Japanese patent publication JP2003-157944 A1).
Another type of contact pin is also disclosed which has a pair of elastic pieces each having a contact portion at its end edge to be contacted to a terminal of the electrical part. At the middle portion of the elastic pieces, bent portions are formed such that bent portions are each bent toward a direction opposite to each other. And when the contact pin is disposed in the socket body, the apexes of the bent portions are pressed by preload means to give a preload to the elastic pieces (Patent document 2: Japanese patent publication JP2000-21531 A1).
However, in such conventional contact pins, a fixed portion of the contact pin is, for example, press-fixed or the like to the socket body so that the fixed portion would not be displaced when the elastic piece extending upward from the fixed portion is elastically deformed. Therefore, much working time is required for mounting the contact pin. Furthermore, the contact pin is usually secured so tightly to the socket body that there is no freedom in changing or adjusting the position or direction of the contact pin after the contact pin is once tightly secured to the socket body. And in a case where positional displacement between the through holes of the socket body and the movable member is occurred due to manufacturing errors, insertion of the contact pin can hardly be carried out smoothly, taking a lot of time in assembling the socket.
In addition, the conventional contact pin is produced by bending a plate-like elastic piece, differences in the shape of the contact pin can be occurred, resulting in a difference in the contact pin's elasticity.
Therefore, when the preload is given to the contact pin as shown in the above mentioned Patent document 2, difference in the amount of preload for each elastic piece is likely to occur, thus being inconvenient and disadvantageous.